It is therefore evident that in order to understand propagation and just what is implied in the act we must make a closer analysis of cell-division, which will be attempted in the next chapters in this book.  

Aside from the complex secondary aid which sex has given to the process of propagation among the higher forms of life, the most important fact which has always led to the conclusion that the two must have an elementary relation is the fact of fertilization.

We might easily understand how species could be propagated without the secondary aid given by sex if it were not for the seemingly elementary act of fertilization.  

In fact, it is well known that among the lower forms the complete propagation of individuals is constantly carried on without an act of fertilization, and this parthenogenetic form is so common that it has always served as the most difficult fact to be harmonized with the theory of the elementary propagating nature of sex and fertilization. That propagation is accomplished in this manner should have suggested to a logical mind that sex and fertilization cannot be an elementary part of the propagating process, but so persistent is a false theory when once firmly rooted into the public consciousness that even some of our most advanced scientists cannot get over the habit of speaking about "Sex Elements."